The invention relates to a method and system for wireline intervention in a subsea well from a floating vessel.
U.S. Pat. No. 6,216,789 describes a method and system for wireline intervention in a subsea well from a floating vessel.
This prior art reference discloses a computer controlled heave compensation wireline logging winch system that compensates for the effects of wave motion on wireline tools suspended from floating vessels. Vessel vertical movement is measured and is physically compensated for by a change in speed of the wireline cable so that the logging data is obtained at a controlled speed. Any error in this physical compensation is detected by a depth measurement system and is used to adjust the true depth at which the logging tool measurements are being recorded.
There is a need to solve two problems associated with the method and system known from U.S. Pat. No. 6,216,789:
(1) Overcome the challenges for upending and overboarding a long, fragile and flexible wireline toolstring from the deck of a floating vessel; and
(2) Accurately heave compensate the toolstring subsea in order to safely stab in the wireline tools into the subsea equipment and control at depth.
Traditionally, subsea well interventions are conducted from heavy-weight, mobile offshore drilling units (MODUs) with riser packages.
Unfortunately, these intervention operations demand substantial operating day rates.
Drilling units offers conventional means to assemble tool string in vertical position and stab in tools through riser packages, therefore heave compensation is usually not an issue. Apart from traditional rig interventions, rigless intervention have been carried out on light intervention vessels that also offers convention ways of assembly and deployment of toolstrings. On those types of vessel, heave compensation is sometimes incorporated to the derrick system itself.
Thus there is a need for an improved wireline intervention method that can be performed from any floating vessel and which does not require use of a large drilling vessel and which overcomes the challenges for upending and overboarding a long, fragile and flexible wireline toolstring from the deck of a floating vessel.